Not least among the radical changes sweeping Russia over the past decade has been the widespread rewriting of history.

Opening secret archives, discarding Marxist cliches and stereotypes, finding vigorous new writers who dare raise long-suppressed questions: All this signifies a gigantic recasting of historical memory, a vast reassessment of the past and a new vision of the future.

Resurrecting hidden documents is necessary but not sufficient. What matters most is replacing traditional Marxist verities with new ideas, new themes - the totalitarian motif, for example, that Western historians have largely discarded, has proved surprisingly popular - that offer satisfying interpretations of the great sweep of Russian history.

The point man in this vast enterprise has been the late Dmitri Volkogonov. As a member of the Soviet establishment; as both a professional historian and a professional soldier of high rank; and as a lieutenant of President Mikhail Gorbachev in the l980s, he could have been expected to play a cautious insider's game. But instead, he created a tremendous stir in Russia with the sharply critical "Stalin: Triumph and Tragedy" (l990). There followed a biography of Lenin (l994), and now, completing the trilogy of the three who made a revolution, Trotsky: The Eternal Revolutionary.

It is an apt title for a carefully written and thoroughly researched work that, addressing a Russian audience, assumes a certain amount of prior knowledge as it raises a vital, transcendent question: How could Trotsky, with all his brilliance, his knowledge of languages, his remarkable verbal and literary fluency, his obvious intelligence, nevertheless insist - despite all factual experience - that world revolution was imminent and indeed certain? What explains this ridiculous obsession, this fanatic insistence that capitalism was soon to disappear?

The answer of course lies deep in Trotsky's psyche, which Volkogonov does not attempt to penetrate. His purpose is, instead, twofold. First, to introduce Russians to a vital historical figure who has been systematically ignored - or denounced - for decades. Second, to shape interpretations, offering analyses and assessments for and against. And here, Volkogonov is solidly on target.

The facts are well-known. They differ only slightly from those surrounding his fellow Old Bolsheviks. Trotsky (1879-1940), the brilliant son of a hard-driving, wealthy Jewish peasant, embraced radical Marxism in his teens, and became a prominent spokesman for the aborted l905 Revolution. There followed prison, exile, journalism, party meetings and maneuvers, the predictable life of a professional revolutionary.

The overthrow of czarism in l917 found him in New York. Returning hastily to St. Petersburg (then Petrograd), he joined Lenin and the Bolsheviks in pressing for another revolution. It came in October, bringing Trotsky international fame as its very symbol, as the tireless agitator, assault commander, and supreme leader, who forced events forward, even as Lenin kept a cautious low profile.

Meanwhile, the czarist Army was disintegrating; achieving peace was vital. Dispatched by Lenin to negotiate with Germany, Trotsky displayed immense ingenuity and tenacity, but could hardly overcome the reality of German power. No matter: Surely the kaiser would soon be overthrown by a vast, all-powerful revolution that would sweep Europe....

Reality was far different, as Volkogonov demonstrates. But Trotsky's reputation was saved by new events, by the civil war sweeping Russia, and by his brilliant work in organizing, equipping and inspiring the Red Army.

That this quintessential civilian should acquire remarkable military skills virtually overnight; that he should lead the Bolsheviks in smashing, now one, now another, White Army; that he should come within an ace of defeating Poland and spreading the revolution to Germany: Did not this demonstrate creative energies amounting to brilliance, even genius?

As befits his own military background, Volkogonov is excellent at assessing this phase of Trotsky's career - as well as the long decline that followed. For decline there was, a decline signified by the slow death of Lenin, and his succession by Stalin in the l920s.

The rise of Stalin as the Communist Party's general secretary, controlling all its appointments and business, drove Trotsky first into irrelevance, then into exile, then to death itself - in l940, at an assassin's hand. Trotsky, a journalist at heart, simply assumed that words and argument would make his case, that he could sway the masses by sheer fluency.

Never did he understand that the platform and printing press could be denied him, and that bureaucratic power could easily trump his arguments. Just how mistaken he was, just how inadequate he proved at the cut-and-thrust of bureaucratic politics la Stalin, became evident with one mistake after another during the last 15 years of his life.

Here is tragedy, all the deeper for its hero's brilliance.

By comparison, Edvard Radzinsky's Stalin, need not be taken seriously. A playwright and television personality in Russia, Radzinsky is skilled at popularizing history, at assembling cliches and stereotypes to produce an overheated and over-emotional text. Much is made of Stalin's surliness, wariness, and inordinate ambition, his grim heritage and outright viciousness. True enough, but hardly a sufficient explanation for what Stalinism signified for the Soviet Union.

Now and again, however, Radzinsky draws on personal memory, family history and a dramatist's instincts to offer momentary insights, not least about the great purges of the l930s.

The letters he draws on by the imprisoned Nikolai Bukharin, one of the most appealing of the Old Bolsheviks, to his wife, tell a grim tale of party loyalty: "Remember that the great cause of the USSR lives on" - sadly reminiscent of "l984." He was executed soon thereafter.